Recently, in the field of automobile production, assembling manipulators have been introduced in order to automate the parts assembling process. For instance, in an assembling process in which a component having a stem and a disc portion at one end thereof, such as intake and exhaust valves of an automobile engine, is clamped by a manipulator hand to be incorporated into a cylinder head, many manipulators have been proposed to accomplish automate the process. Japanese Patent Public Disclosure No. 60-238237, laid open to the public on Nov. 27, 1985, proposed an assembling manipulator by which a valve disc is suctioned by negative pressure to a manipulator hand so that the valve can be incorporated into a cylinder head. However, the disclosed manipulator does not provide a mechanism for positioning the valve disc and manipulator hand. Since the valve must be centered when the valve disc is suctioned to the manipulator hand, the lack of a mechanism for positioning the valve disc and manipulator hand may impede centering accuracy so that it is difficult to effectively automate the assembling process.